1. Field of the Invention
The present invention relates to a stabilizer against hydrolysis for an ester-group-containing resin and a thermoplastic composition containing the same. More specifically, the present invention relates to a stabilizer against hydrolysis comprising a carbodiimide composition containing an aliphatic carbodiimide compound and a phosphorus antioxidant, preferably a stabilizer against hydrolysis comprising a carbodiimide composition wherein a phosphorus antioxidant is dispersed and compounded therein by admixing the phosphorus antioxidant in a raw material of an aliphatic carbodiimide compound in advance, and a thermoplastic resin composition containing the same.
2. Description of the Prior Art
A carbodiimide compound has been widely used as a stabilizer against hydrolysis for an ester-group-containing resin or a biodegradable plastic (see, JP-A-11-80522 and A-2002-187965).
However, a compound with low molecular weight such as a monocarbodiimide had problems such as causing environmental pollution by generating a component having an offensive odor or losing the addition effect thereof by vaporization, because of based on a tendency for easy thermal decomposition during processing.
Polycarbodiimide has been used to solve these problems, but use of this compound is difficult for an application where hue is seriously considered (for example, application to clothing fiber) due to the yellowing problem during processing.
The above-described-ester-group-containing resin includes, for example, a polyethylene terephthalate resin, a polybutylene terephthalate resin, a polyester polyurethane resin, an unsaturated polyester resin, a maleic resin, an alkyd resin, a polycarbonate resin, a polyester carbonate resin, an aliphatic polyester resin, polyether esters, polyesteramides and polycaprolactones.
Further, biodegradable plastics can roughly be classified to aliphatic polyesters having polyester groups in their molecular chains (including those produced by microorganisms), natural polymers such as cellulose, polysaccharides produced by microorganisms, polyvinyl alcohol (PVA) and polyethers such as polyethylene glycol (PEG).
Among them, polylactic acid of an aliphatic polyester as a plastic material derived from plants, and with there being increasing interest on global environment problems such as CO2 reduction has been extensively studied in commercial fields such as automotive parts, housings of home electric appliances and clothing.
However, the above-described resin having ester groups (ester-group-containing resins) and a biodegradable plastic have poor stability against hydrolysis. In particular, a biodegradable plastic including an aliphatic polyester has significantly poor stability, which has made it difficult to use these materials in applications with the same levels of functions (such as strength, water resistance, moldability and heat resistance) as those required of conventional plastics.
From these circumstances, several proposals relating to improvement of stability against hydrolysis of an ester-group-containing resin or a biodegradable plastic have been made. For example, proposals disclosed include one directed to a method for controlling a biodegradation rate of a biodegradable plastic (see, for example, JP-A-11-80522 and JP-A-2001-525473), or another one directed to a method for stabilizing against hydrolysis of an ester-group-containing resin (see, for example, JP-A-9-296097 and JP No. 3,122,485).
In spite of these proposals, the above problems of a carbodiimide compound have not sufficiently been solved in applications where hue is seriously considered, such as fibers, films and sheets, because of the high yellowing of a carbodiimide compound when utilized as a stabilizer against hydrolysis, added to an ester-group-containing resin or a biodegradable plastic.